There are a variety of conditions which result in pathologic chronic collection of bodily fluids within the peritoneum, pleura or pericardial sac. Chronic ascites, pleural effusion and pericardial effusion are conditions in which chronic fluid collections persist and result in increased morbidity and mortality.
These foregoing conditions currently are treated typically by one of three methods: 1) external drainage, which poses a risk of infection and long-term requirement for multiple punctures, 2) drainage to another body cavity, or 3) treatment with drugs. In pleural effusion, excess fluid arising from an underlying pathology, such as lung cancer, breast cancer or lymphoma, accumulates in the pleural cavity. If left untreated, the fluid accumulation may interfere with proper lung function, significantly increasing morbidity and mortality. Depending upon the underlying cause of the pleural effusion, treatment may consist of drug therapy, thoracentesis, in which a needle is periodically inserted through the chest and into the pleural cavity to drain the fluid accumulations, or installation of an intercostal drain, in which one end of a pigtail catheter is inserted into the pleural cavity and the fluid is drained to an external canister. Although a relatively simple procedure, placement of an intercostal drain is associated with a relatively high rate of major complications, including hemorrhage and infection. Repeated effusions also may be treated by pleurodesis, in which two pleural surfaces are attached to one another so that no fluid can accumulate between them. However, this procedure requires a lengthy hospital stay and is reported to be associated with the onset of adult respiratory distress syndrome, a potentially life-threatening complication.
In pericardial effusion, fluid accumulates in the pericardial sac and may lead to increased intrapercardial pressure and reduced cardiac output. Where the fluid accumulation interferes with proper heart function, pericardiocentesis may be performed, in which the fluid is drained to an external site through a needle or catheter inserted through the chest wall and into the pericardial sac. For chronic cases, the treatment of choice is formation of a pericardial window. In this highly invasive procedure, a section of the pericardial sac is removed to create a fistula that permits fluid to drain to the abdomen. Although this procedure is usually well tolerated by patients, the pericardial window may close, requiring re-operation.
Ascites is a highly debilitating complication associated with many medical conditions including liver failure, congestive heart failure and certain cancers. Untreated ascites can result in respiratory compromise, compression of the inferior vena cava (a vital blood vessel) and spontaneous bacterial peritonitis (a life-threatening condition). Conventional treatment for ascites includes a regime of drugs and dietary restriction, and for chronic cases, repeated surgical interventions.
The drugs often employed to treat ascites are usually long-term and often result in complications. The most common pharmaceutical treatment of ascites involves the use of diuretics to remove fluid from the patient's body through their urine. The difficulty with this treatment, however, is that fluid is removed from the entire body, including the circulating volume of blood. This in turn may result in excessive loss of fluid required to perfuse the vital organs of the human body. Thus, even with frequent application, the medicines frequently provide unsatisfactory results. In such cases, surgical, or invasive, procedures are indicated.
For chronic ascites refractory to drugs, a patient typically is required to undergo paracentesis on a regular basis, e.g., every 2-4 weeks, to drain accumulated fluid. In this procedure, peritoneal fluid is drained through the abdominal wall via the insertion of a needle through the abdominal wall into the peritoneal cavity. The regular accumulation and drainage by paracentesis of large quantities of fluid in the peritoneal cavity adversely impacts patient quality of life and often can interfere with the patient's ability to combat the underlying disease, such as cirrhosis. Moreover, repeated paracenteses place the patient at increased risk for a life-threatening infection of the peritoneal cavity. Other surgical/invasive procedures typically involve treatment of the cause of the ascites (for example, the Transjugular Intrahepatic Portosystemic Shunt) but these measures also frequently result in serious and life-threatening complications or become ineffective over time. Consequently, such procedures are performed infrequently.
Paracentesis often provides only a temporary solution in chronic cases, as the ascites quickly refills the peritoneal cavity. In particular, the presence of large quantities of fluid within the peritoneal cavity frequently disturbs the patient's fluid equilibrium, such that the patient's body attempts to compensate for fluid loss due to paracentesis by increasing ascites production. To combat this phenomenon, it is standard practice for clinicians to infuse a plasma expander, usually human albumin, into patients undergoing paracentesis. The cost of human albumin used for a typical 5-7 liter extraction can cost upwards of $500 per procedure. Consequently, regularly scheduled paracenteses followed by infusion of human albumin impose significant economic burdens on the patient and the health care system.
Previously known attempts to treat ascites have included indwelling catheters including external ports, and squeeze-bulb and magnetically-driven reciprocating pumps to transfer ascites from the peritoneal cavity into the venous vasculature, through an external port, or into the bladder. For example, U.S. Pat. No. 4,240,434 to Newkirk and U.S. Pat. No. 4,657,530 to Buchwald each describes a squeezable tube-type ascites shunt having an inlet end configured to the placed in the peritoneal cavity and an outlet end configured to be placed in a vein. Rosenblit et al., in an article entitled “Peritoneal-Urinary Drainage for Treatment of Refractory Ascites: A Pilot Study,” J. Vascular & Interv. Radiology, 9(6):998-1005 (November/December 1998) describe a similar squeeze-bulb system having an outlet disposed in the bladder. U.S. Pat. No. 4,610,658 to Buchwald et al. describes an implantable pump for treating ascites that includes a magnetically-driven pump to transfer fluid from the peritoneal cavity to the vasculature system. Such previously known devices suffer from a variety of drawbacks, including fibrous encapsulation, frequent clogging and infection. Such devices provided little improvement over periodic paracenteses, and resulted in increased rates of infection, re-operation or other complications if left in place for any length of time. Moreover, a key drawback of such previously-known systems is the requirement that the patient must repeatedly locate and manually actuate the pumping mechanism on a daily basis. Such activity may be difficult for patients, especially the elderly and obese, and further complicated by an ascites-distended abdomen. Consequently, the difficulty of manipulating such previously-known systems promotes patient non-compliance, in turn leading to clogging and infection.
In view of the above-noted drawbacks of previously-known systems, it would be desirable to provide methods and apparatus for treating ascites that remove small quantities of fluid multiple times per day, and thereby avoid fluid disequilibrium caused by periodic removal of large volumes of fluid using paracentesis and concomitant use of costly plasma expanders.
It further would be particularly desirable to provide methods and apparatus for treating ascites and other intracorporeal fluid accumulations using implantable devices that are resistant to clogging, reduce risk of infection, and do not interfere with normal working of a patient's vascular system.
It also would be particularly desirable to provide methods and apparatus for treating ascites and other intracorporeal fluid accumulations using implantable devices that are configured to pump at high flow during multiple intervals daily, thereby reducing the risk of pump or catheter blockage.
It still further would be desirable to provide methods and apparatus for treating ascites and other intracorporeal fluid accumulations using implantable devices that are capable of sensing environmental conditions and that move fluid only when doing so is consistent with a patient's activity level.